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Thread: Aerosucre B-727 crash

  1. #61
    Senior Member Gabriel's Avatar
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    Do you guys realize that this article that triggered such an animated discussion here, and the preliminary report it is based on, are both from Feb 2017???? (that is, one year old)

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  2. #62
    Senior Member Gabriel's Avatar
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    Quote Originally Posted by Schwartz View Post
    forward drag
    Does drag come in any flavor other than "forward"?

    (answer: no, as long as we understand "forward" as "in the direction of motion". The very definition of drag is the total aerodynamic force parallel to the airspeed vector, and if you change parallel by perpendicular you get lift)

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  3. #63
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    Oh geez... next you're going to try to tell us that when you step on the brake pedal in your car, what happens is not "deceleration" but acceleration toward the rear...
    Be alert! America needs more lerts.

    Eric Law

  4. #64
    Senior Member 3WE's Avatar
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    Quote Originally Posted by Evan View Post
    Flaps aren't about gaining lift, they're about allowing the plane to fly at slower speeds.
    Ok...oh great one...how do you fly at a lower speed and get the same lift as at a higher speed? You generate more lift per speed.

    And why do we even use them at all for takeoff?

    General fundamental rule: Lower flap settings provide a good amount of lift increase with an acceptable amount of drag. Higher flap settings tend to produce less 'additional' lift, but a fair bit more drag.

    Then, let's discuss the 727...an aircraft with some of the biggest, most intricate flaps that were designed to give the aircraft impressive short-field performance...It is so very amazing how they keep moving backwards and increasing wing area...It would not surprise me that you pick up a good bit more 'effective wing area' when going between a 20 and 30 degree setting.

    Flaps...short field performance...interesting concept.

    Another fundamental rule: Flaps often shorten the ground roll (but sometimes at the expense of rate of climb). I dunno, are we dealing with a short field situation here?

    And even one more: There's this thing called ground effect...I wonder if the interaction of flaps and ground effect might not give you even MORE lift and MORE ability to clear the airport fence and hopefully a small building or two (acknowledging that there are ultimate limits to everything).

    Exactly how much is each affected?- what is the magical flap setting for the best balance?...what is the magical setting for a particular situation?...runway length vs. climb requirement... (Yeah you will try to bring up a climb gradient here...the brick hut seemed to be a challenge...but the 'climb gradient' of the terrain in the youtube looks fairly reasonable.)

    Should one read the FCOMPOHQRH for exactly the best flap setting for the runway and temperature and wind and weight?...yeah...But I have one beer (yes, only one beer) that 30-degrees of flaps on a 727 might be within 3 degrees of 'ideal' for the shortest ground roll performance (and I say that due to 727 flaps being full of super-duper-high-lift-scientific engineering). That is probably not a great setting for a 172...but then again, if I only need to get off the ground, and don't even have to clear a 3-strand barb wire fence...maybe the flaps will get me off sooner...

    Did this crew read the FCOMPOHQRH for the best takeoff setting?...I don't know if they did that day before that takeoff, but I'm thinking it was read on occasion and data from it used so that every other takeoff before this one was accomplished with perfection...

    By the way- very few of the people reading this thread will see the immense beauty that is demonstrated here:

    https://www.youtube.com/watch?v=qDs7haZK7Go
    Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

  5. #65
    Senior Member Evan's Avatar
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    Quote Originally Posted by 3WE View Post
    Ok...oh great one...how do you fly at a lower speed and get the same lift as at a higher speed? You generate more lift per speed.

    And why do we even use them at all for takeoff?

    General fundamental rule: Lower flap settings provide a good amount of lift increase with an acceptable amount of drag. Higher flap settings tend to produce less 'additional' lift, but a fair bit more drag.

    Then, let's discuss the 727...an aircraft with some of the biggest, most intricate flaps that were designed to give the aircraft impressive short-field performance...It is so very amazing how they keep moving backwards and increasing wing area...It would not surprise me that you pick up a good bit more 'effective wing area' when going between a 20 and 30 degree setting.

    Flaps...short field performance...interesting concept.

    Another fundamental rule: Flaps often shorten the ground roll (but sometimes at the expense of rate of climb). I dunno, are we dealing with a short field situation here?

    And even one more: There's this thing called ground effect...I wonder if the interaction of flaps and ground effect might not give you even MORE lift and MORE ability to clear the airport fence and hopefully a small building or two (acknowledging that there are ultimate limits to everything).

    Exactly how much is each affected?- what is the magical flap setting for the best balance?...what is the magical setting for a particular situation?...runway length vs. climb requirement... (Yeah you will try to bring up a climb gradient here...the brick hut seemed to be a challenge...but the 'climb gradient' of the terrain in the youtube looks fairly reasonable.)

    Should one read the FCOMPOHQRH for exactly the best flap setting for the runway and temperature and wind and weight?...yeah...But I have one beer (yes, only one beer) that 30-degrees of flaps on a 727 might be within 3 degrees of 'ideal' for the shortest ground roll performance (and I say that due to 727 flaps being full of super-duper-high-lift-scientific engineering). That is probably not a great setting for a 172...but then again, if I only need to get off the ground, and don't even have to clear a 3-strand barb wire fence...maybe the flaps will get me off sooner...

    Did this crew read the FCOMPOHQRH for the best takeoff setting?...I don't know if they did that day before that takeoff, but I'm thinking it was read on occasion and data from it used so that every other takeoff before this one was accomplished with perfection...

    By the way- very few of the people reading this thread will see the immense beauty that is demonstrated here:

    https://www.youtube.com/watch?v=qDs7haZK7Go
    First of all, the B727 is not what you might call a STOL aircraft. Maybe a SHL (Short Hard Landing) aircraft if you used that 40 setting at the wrong moment.

    Flaps 30 is full landing flaps for most operations. It is essentially a speed brake.

    Flaps 40 is essentially a drogue chute. Some major airlines had this setting blocked because of fuel usage and noise abatement. It could also lead to dangerous sink rate. It wasn't needed.

    So, selecting flaps 30 is selecting full landing configuration for take-off.

    UNLESS that modification Gabriel speaks of positions flaps 30 differently for takeoff than for landing. That is the only way I can make sense of it.

    Still, flaps 25 should give you plently of short field performance.

    I have to do more research on this STC ST00507SE...

  6. #66
    Senior Member Gabriel's Avatar
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    Guys, apparently this was a legal (I am not saying "smart") take-off configuration. Hopefully it was also a legal one for this particular take-off.
    Any take-off configuration and power setting will put you at not less than V2 and not less than 35ft above the departure end of the runway after losing an engine at V1. This airplane did not lose an engine (until impacting the hut), the hut was hundreds of feet past the departure en of the runway, and the hut was much less than 35 ft tall. In any acceptable take-off configuration and setting this plane should have cleared the hut by 100 ft or more.

    The flap setting could explain a low climb gradient but should also provide a lower Vr and hence earlier rotation, the plane rotates near the end of the runway what makes me think that the flap setting was not the main issue, and then even when well nose-up it fails to climb what means that it was rotated at a lower speed than required for the weight and confing. This plane was overweight or underpowered for the available take-off distance (TODA). Or both. Flaps setting is secondary.

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  7. #67
    Senior Member 3WE's Avatar
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    Quote Originally Posted by Gabriel View Post
    Guys, apparently this was a legal...take-off configuration.... Flaps setting is secondary.
    Concur

    Oh, and 25 degrees is ok, but 30 is too much...okay.
    Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

  8. #68
    Senior Member Evan's Avatar
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    Quote Originally Posted by Gabriel View Post
    The flap setting could explain a low climb gradient but should also provide a lower Vr and hence earlier rotation, the plane rotates near the end of the runway what makes me think that the flap setting was not the main issue, and then even when well nose-up it fails to climb what means that it was rotated at a lower speed than required for the weight and confing. This plane was overweight or underpowered for the available take-off distance (TODA). Or both. Flaps setting is secondary.
    However, Vr being a speed and not a place on the runway, and flaps 30 being a speed brake, could that be a factor in pushing Vr further down the runway?

    I'm beginning to wonder about the accuracy of that report. The Quiet Wing modification is apparently centered around adding slight droop to the configuration (1-4deg of flap and aileron) to improve performance. I don't see anything about it enabling a 30deg takeoff configuration (remember, that would require meeting the requirements of the 14 CFR Part 25 Section 121 for certification). I think something has been lost in translation here...

  9. #69
    Senior Member Gabriel's Avatar
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    Quote Originally Posted by Evan View Post
    However, Vr being a speed and not a place on the runway, and flaps 30 being a speed brake, could that be a factor in pushing Vr further down the runway?
    No way. It is still a slow speed regime where the parasite drag is low and, only once the plane is flying the induced drag is high. Up to the rotation point, the parasite drag is low, the induced drag is almost nonexistent (the wing is making small amounts of lift), and you have 3 engines at take-off power that are good enough to climb 3000 fpm with the more parasite drag, plus a big induced drag, plus against gravity (component of the wight in the direction of the airspeed, i.e. upslope).

    As a comparison, if you don't use the brakes, the spoilers doesn't help you a lot to reduce the speed. They only work because they kill lift (actually make it negative) greatly increasing the weight-on-wheels and hence the brake effectiveness.

    I'm beginning to wonder about the accuracy of that report. The Quiet Wing modification is apparently centered around adding slight droop to the configuration (1-4deg of flap and aileron) to improve performance. I don't see anything about it enabling a 30deg takeoff configuration (remember, that would require meeting the requirements of the 14 CFR Part 25 Section 121 for certification). I think something has been lost in translation here...
    The rumors I saw in the net say the flaps and ailerons are re-rigged so when retracted they are between 3 and 7 degrees down (I think starting from 7 in the inside flaps to 3 in the outside flasp, and I don't know if the slow speed ailerons are also involved). That would give you an average 0 setting of actually 5 degrees, so a 25deg take-off setting (which I think is a valid short-runway setting) becomes about 30. But again, in this instance I really don't know what I am talking about, just spreading rumors seen elsewhere in other fora.

    We will likely will know.... just wait for the final report

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  10. #70
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    Quote Originally Posted by Gabriel View Post
    Do you guys realize that this article that triggered such an animated discussion here, and the preliminary report it is based on, are both from Feb 2017???? (that is, one year old)
    Yep, I noticed when I looked it up. I came across the video on YouTube and then I thought I would look up what some of the findings were remembering it was discussed here.

  11. #71
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    Quote Originally Posted by Gabriel View Post
    Does drag come in any flavor other than "forward"?

    (answer: no, as long as we understand "forward" as "in the direction of motion". The very definition of drag is the total aerodynamic force parallel to the airspeed vector, and if you change parallel by perpendicular you get lift)
    OK, fair, although I think the opposite of sideways drag comes into play in crosswinds...

  12. #72
    Senior Member Gabriel's Avatar
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    Quote Originally Posted by Schwartz View Post
    OK, fair, although I think the opposite of sideways drag comes into play in crosswinds...
    What? (yes, I did note the )

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  13. #73
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    Quote Originally Posted by Evan View Post
    First of all, the B727 is not what you might call a STOL aircraft. Maybe a SHL (Short Hard Landing) aircraft if you used that 40 setting at the wrong moment.
    From what I was reading the 727 is very popular around the world due to it's ability to use short runways.

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    Quote Originally Posted by Gabriel View Post
    What? (yes, I did note the )
    Perhaps a better pedantic example: The term "forward" refers to the orientation relative to the pilot rather than the direction of motion. i.e. a plane that stalled at high altitude, lost all foward motion and was travelling straight down while still being oriented to the horizon, would be generating downward drag because the direction of movement was down given the orientation of the pilot and passengers.

  15. #75
    Senior Member 3WE's Avatar
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    Quote Originally Posted by Schwartz View Post
    From what I was reading the 727 is very popular around the world due to it's ability to use short runways.
    Yes...but the black and white acronym department doesn’t like relative runway requirement comparisons- the concept confuses them.
    Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

  16. #76
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    Quote Originally Posted by 3WE View Post
    Yes...but the black and white acronym department doesn’t like relative runway requirement comparisons- the concept confuses them.
    As yes, so very confusing! The common definition of STOL is the ability to go from the start of the take-off roll to V2 (50' above obstacles) in the very black and white distance of 1500ft!

    An empty 727-200ADV can get out of a 4000' runway. That is relatively good short-field perfomance, But at MTOW is needs about 10,000ft. I suspect this one was more in the latter category.

    My point being, the popular myth the the 727 was some sort of STOL-esque passenger jet is a bit misplaced.

  17. #77
    Senior Member 3WE's Avatar
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    Quote Originally Posted by Evan View Post
    As yes, so very confusing! The common definition of STOL is the ability to go from the start of the take-off roll to V2 (50' above obstacles) in the very black and white distance of 1500ft!

    An empty 727-200ADV can get out of a 4000' runway. That is relatively good short-field perfomance, But at MTOW is needs about 10,000ft. I suspect this one was more in the latter category.

    My point being, the popular myth the the 727 was some sort of STOL-esque passenger jet is a bit misplaced.
    Here’s a fun exercise...go see if Schwartz or I ever said, “The 727 was designed to be an official FAA acronym defined STOL aircraft”.

    Per usual, it’s a challenge for you to comprehend that the aircraft might have been designed to operate in a gray area of offering better takeoff performance and runway flexibility than a 707 or DC-8...the flexibility to serve smaller cities with smaller airports (more gray areas for you.)

    Unfortunately the acronym ITPARFVSOSADCE and associated requirements were never developed to allow you to understand some of the design considerations for DC-9 and 727 aircraft.

    https://youtu.be/OZ6M5heqC9Y

    I look forward to a video of a 707 or DC-8 operating on gravel...I’m fairly confident that happens less often.
    Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

  18. #78
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    Quote Originally Posted by 3WE View Post
    Here’s a fun exercise...go see if Schwartz or I ever said, “The 727 was designed to be an official FAA acronym defined STOL aircraft”.

    Per usual, it’s a challenge for you to comprehend that the aircraft might have been designed to operate in a gray area of offering better takeoff performance and runway flexibility than a 707 or DC-8...the flexibility to serve smaller cities with smaller airports (more gray areas for you.)

    Unfortunately the acronym ITPARFVSOSADCE and associated requirements were never developed to allow you to understand some of the design considerations for DC-9 and 727 aircraft.

    https://youtu.be/OZ6M5heqC9Y

    I look forward to a video of a 707 or DC-8 operating on gravel...I’m fairly confident that happens less often.
    PS- Are the MTOW performance figures relevant for a 1968 flight from Little Rock to Chicago? There’s that OTHER gray concept of flexibility- fill the tanks, max it out, do the LTOL thing and fly a load of buttocks across a pond.
    Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

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